In vehicles with a seat means of the above type, it is common to in particular the rear seat of the vehicle or car have the back supporting portion thereof releasably lockable to a body part of of the vehicle or car. Such car may be of the saloon, hatchback or estate type.
If the back supporting portion is not properly locked to the body part, there will be no indication of insufficient interengagement between the first and second lock means. In a situation of in particular a head-on car collision, this may be fatal to the health of rear seat passengers and might also involve a risk to the health of the car driver or a front seat passenger. The hazard situation is two-fold. Firstly, a non-secured seat lock means implies that in a situation of collision, the back supporting portion--if tiltable relative to the body part or the sitting portion of the seat--will push heavily on the back seat passenger with a force being a high multiple of the weight of the back supporting portion. Secondly, if the car has luggage in the boot or luggage space, the luggage will move forward with a force being a high multiple of its weight. Thus, as the back supporting portion does not offer any substantial resistance against the high force exerted by the forward moving luggage, this means that the rear seat passengers will receive from behind an extremely high dynamic force load, which combined with the forces exerted over the passenger front portion due to the car seat belts, could cause vital passenger injury or even cause passenger death. In case the car or vehicle has no rear seat passengers to effectively counteract such forwardly directed forces from back supporting portion or from rapidly forward moving, unsecured luggage, then the situation may be quite hazardous to a front seat passenger or a car driver. Provided the car has luggage, the luggage will effectively "fly forward" and in the best of situations hit the rear of the back supporting portion of one or both front seats. However, in view of the rear back supporting portion(s) tilting forward, such portion may not necessarily assume a horizontal position, but rather form a ramp for the rapidly forward moving luggage, thus involving the added risk of hitting an upper past of the front seat back supporting portion or even the head or neck region of the driver and/or passenger, involving the obvious risk of causing vital or fatal injury to the person involved.
Further, it should be appreciated that with a back supporting portion strecthing over the full internal width of the car, it is not sufficiently only to have the lock means on one side of the car securely locked, when the lock means on the other side of the car is not properly locked.
Thus with the ever growing use of forwardly tiltable or movable back supporting portions of rear seats in estate, saloon or hatchback cars, there is an obvious need for some means to prevent the hazard caused by the first and second lock means not being fully secured.